A pre-chamber sparkplug comprises, among other things, a central electrode and at least one ground electrode, which is arranged at a distance from the central electrode with the formation of a spark gap. The central and the ground electrode are arranged inside the pre-chamber cap. The compressed gas-air mixture flows into the pre-chamber via one or more transfer bores in the pre-chamber. After ignition, this mixture then spreads the flame front from the pre-chamber through these transfer bores into the main combustion chamber.
For example, a first embodiment DE 101 44 976 A1 shows a pre-chamber sparkplug with an annular ground electrode, which is fastened via fasteners at the pre-chamber cap. In the longitudinal direction of the pre-chamber the ground electrode shows an internal and an external circumferential area. The internal circumferential area faces the central electrode. The external circumferential area is arranged on the side of the ground electrode, which faces away from the central electrode. In a second embodiment several ground electrodes are arranged radially facing the central electrode. In both embodiments the central and the ground electrode are not accessible from the outside. Accordingly, both the volume burned off and the life span of the pre-chamber sparkplug is predetermined here. The volume burned off results from the minimal distance of the ground electrode from the central electrode in the new condition of the pre-chamber sparkplug as well as from the maximum distance and the shape of the ground electrode. Furthermore, the annular ground electrode cannot be adjusted, even if the pre-chamber were accessible. The life span of such a pre-chamber sparkplug typically amounts to approximately 2000 operating hours, so that here potentials are given for optimization.
Accordingly, there exists a need to further increase the life span of a pre-chamber sparkplug.